This invention relates generally to an elevator, and more specifically to method and apparatus for determining the position of an elevator car as the car moves along a hoistway.
In order to bring an elevator car to a smooth, safe stop, level with a landing, the car controller must have reliable information concerning the movement and position of the car in order to know when to initiate car leveling and stop procedures as well as the opening the car doors. To carry out these functions accurately, it is necessary to know the car""s exact position at all times.
Many existing reference systems are based on incremental encoders and vanes which can be mounted in a variety of arrangements within the hoistway. In one arrangement, an endless tape having slots formed along its length is attached to the car and is trained about idler sheaves located at the top and the bottom of the hoistway. One sheave contains teeth that mate with the slots in the tape so that the sheave is driven by the endless tape. An encoder is driven by the toothed sheave and provides primary car position information to the car controller. Additional discrete position sensors and vanes are located at each landing to provide secondary car position information that is used to bring the car to a smooth, safe stop at each landing.
A second widely employed position determining system involves an encoder that is mounted upon the shaft of the elevator drive motor. Car position data is determined by the encoder unite and is processed and used to derive the car speed and the distance to a landing information concerning the various floors. Additional sensors and vanes are again needed at each landing and the position of the elevator car as derived by the encoder is checked and corrected if needed each time the car passes a vane at a landing.
Although these existing systems work well in practice, they have certain drawbacks in that most prior art systems of this type are relatively expensive to install, and are difficult to adjust and costly to maintain. Error correction is also necessary at each landing in order to compensate for rope slippage or the like. The car""s position relative to the landings is generally measured indirectly by an encoder and the position information is acquired incrementally. This data, therefore, must be saved in memory in case of a system shutdown. This, in turn, requires the use of batteries to power the memory during a shutdown. When position data is lost, correction runs must be carried out to reestablish position references and the system must be recalibrated often as the building housing the elevator system settles. Finally, as noted above, most prior art position reference systems require redundant position sensors and vanes at the landings to insure positive detection of the car, as it approaches the landings.
It is therefore an object of the present invention to improve elevators, and, in particular, to improve positioning systems used to control elevators.
It is a further object to provide a non-contact absolute positioning system for an elevator that will not be adversely affected by side-to-side or front-to-back movement of the elevator car.
A still further object of the present invention is to eliminate the need for correction runs and recalibration of an elevator position system after a power loss.
Another object of the present invention is to reduce the cost of installing and maintaining an elevator system.
Yet another object of the present invention is to provide a redundant speed measuring system for an elevator without the need of providing additional encoders.
Yet a further object of the present invention is to continually correct an elevator positioning system as a building in which the system is housed settles.
These and other objects of the present invention is attained by a system for determining the position of an elevator car within a hoistway in which the elevator car is mounted for reciprocal movement. In one form of the invention, a vertically disposed code rail containing optically discernable information is mounted within the hoistway adjacent to the car""s path of travel. An optical sensor is mounted upon the car for movement therewith. The sensor is positioned to optically read code rail indicia related to the hoistway and feed this information to the car controller. The code rail can be a continuous strip running along the vertical length of the hoistway or code rail indicia on independent code rail sections, each of which being located at a particular landing.
In another form of the invention, a single sensor is arranged to read a code rail strip extending along the length of the hoistway to acquire primary position data and at the same time, read individual code rail sections at each landing to acquire secondary position data.
In a further embodiment of the invention, two sensors are secured to the elevator car in vertical spaced apart alignment and arranged to read two vertically separated code rail sections simultaneously to acquire a range of position related information.